Coated abrasive back-up pads are known which include a support surface to which sheets having coated abrasive material on one surface and pressure sensitive adhesive on the other may be releasably adhered. Typically the support surface is on a flexible polymeric adhesion layer attached to one surface of a layer of resiliently compressible foam, and the back-up pad has a rigid backing plate attached to an opposite surface of the layer of foam and adapted to be attached to a drive mechanism by a circular array of screws so that the drive mechanism can be used to drive the pad and thereby the abrasive against a surface to be abraded while the layer of foam provides a flexible cushion that causes the abrasive to follow and level the contour of that surface. In one eight inch diameter embodiment of such a back-up pad commercially available from National Detroit, Detroit, Michigan, the backing plate is of aluminum which can bend if the pad is dropped or otherwise impacted edgewise against a solid surface; whereas in another commercially available from Eezer, Fresno, Calif., the backing plate is of a fiber reinforced polymeric material (i.e., fiberglass reinforced epoxy) which can withstand such impacts, but is sufficiently brittle that flexing of the backing plate with the foam layer can cause the screws to break through the backing plate or to break away portions of the backing plate, thereby causing the back-up pad to come loose from the drive mechanism.
Additionally, the screws that attach the backing plate to the drive mechanism are attached or removed through access holes through the adhesion layer and the layer of foam. The portion of the pad around these access holes presents two problems. Removal of numerous sheets of abrasive material from the support surface can pull the edge of the adhesion layer away from the foam and eventually cause portions of it to break away. Also, molding the access holes in the layer of foam causes a foam skin layer around the access opening that is less flexible than adjacent portions of the foam. Thus areas of greater pressure are provided around the access openings when the pad is used to press moving abrasive material against a surface that can result in uneven grinding of a workpiece.